Automobile receiver volume control circuit



1388- 1940- J. HATHAWAY AUTOMOBILE RECEIVER VOLUME CONTROL CIRCUIT FiledSept. 25, 1939 INVENTOR. Jig HA THA W4 Y ATTORNEY.

QM: mum Q\QV Q P wags in E W l 62m w 7 H HBQSQSW I I I I I I I I I I I iI I I r q Q 1 A {w Patented Dec. 10, 1940 UNITED STATES PATENT OFFICEJarrett L. Hathaway, Manhasset, N. Y., assignor to Radio Corporation ofAmerica, a. corporation of Delaware Application September 23, 1939,Serial No. 296,183

8 Claims.

My present invention relates to radio receivers adapted for mobilevehicles such as automobiles. and more particularly to automaticcircuits for controlling the volume of a radio receiver installed in anautomobile.

Various systems have been developed in the past for relating in anautomatic fashion the volume level of a radio receiver installed in anautomobile and the noise level produced by movement of the latter. Inall of these systems it has been the essential object to increase thevolume of the receiver as the speed of the car increased. This was donebecause of the increase in intensity of the general noises inherent in aspeeding automobile. In general, such noises are wind noises, rattlingof mechanical parts of the car, the noise of the speeding engine, theincreased volume level of the voices of the persons riding in a fastmoving automobile. Many of these prior systems depend upon increase inair pressure due to the increased speed of the automobile.

One of the main objects of my present invention is to control the volumeof an automobile radio receiver as a function of engine speed, and thegain control voltage being effectively derived from the ignition systemof the automobile.

Another important object of the invention is to provide in combinationwith the radio receiver of an automobile a gain control system whichutilizes a unidirectional voltage derived from a rectifier within theradio receiver, the rectifier being actuated by pulses from the ignitionsystem.

Still another object of the invention is to provide a receiver gaincontrol arrangement for an automobile radio receiver wherein voltagepulses feeding the gain control rectifier are derived from at least oneof the spark plugs of the automobile engine, and the unidirectionalcontrol voltage developed is a function of the speed of the engme.

Still other objects of my invention are to improve generally thesimplicity and efiiciency of gain control circuits for automobile radioreceivers, and more especially to provide an automobile receiver gaincontrol arrangement which is not only reliable in operation, but iseconomically manufactured and assembled in a receiver.

The novel features which I believe to be characteristic of my inventionare set forth in particularity in the appended claims; the inventionitself, however, as to both its organization and method of operationwill best be understood by reference to the following description takenin connection with the drawing in which I have indicateddiagrammatically a circuit organization whereby my invention may becarried into effect.

Referring to the drawing, there is shown in schematic fashion my presentinvention as applied to a receiver of the type installed in anautomobile. Let it be assumed that the networks located within thedotted line rectangle provide a radio receiving system of any well knowntype usually installed in an automobile. Such receivers are very wellknown at this time, and usually they are of the superheterodyne type.The number I denotes any well known type of signal collector device, andthe latter may be of the rod type, or of the type wherein a plate isspaced from the undersurface of the running board. Regardless of theconstruction of the signal collector, there is utilized a radiofrequency selection and amplification network 2. Where the receiver isof the superheterodyne type, such a network 2 will comprise one or moretunable radio frequency amplifiers feeding a tunable first detector, anda tunable local oscillator feeding the local oscillations to the firstdetector. Additionally, the network 2 may include one or more stages ofintermediate frequency amplification. The numeral 3 denotes the usualsecond detector of the superheterodyne receiver, and numeral 4designates the first audio amplifier tube which has impressed upon itssignal grid 5 the audio frequency voltage output of the detector 3.

While the tube 4 is shown as of the pentode type, it is to be understoodthat any other type of tube adapted for audio frequency amplificationcan be used. The amplified audio voltage is then transmitted through anyother well known audio utilization network, and finally is reproduced bya loudspeaker. The cathode circuit of tube 4 may be grounded directly,or connected to a point of suitable potential. The control grid 5 isreturned to a point of negative potential through a path which includesa potentiometer tap 5, resistor 3, tap 1 and rectifier load resistor ll.Potentiometer 3-5' is in the grid return circuit of tube 4, serving as amanual volume control. The low potential side of 3 is by-passed foraudio frequencies by means of condenser 6.

The rectifier 8 has impressed upon its cathode 9, voltage pulses derivedfrom the ignition system of the automobile, a suitable means being oneof the spark plugs of the automobile engine. The anode '0 of the diodeis at a negative bias potential, and the cathode 9 and anode Ill of thediode are connected by resistors II and I2, the former of which developsthe direct current voltage employed for gain control of audio amplifier4. A potentiometer, which comprises the slidable tap 1 which isadjustable along load resistor functions to compensate for differencesin automobiles and ignition systems. The resistor I2 and condenser l3provide the usual time constant network. Condenser 30 is of smallcapacity, allowing the cathode 9 to attain a D. C. (direct current)potential, but at the same time said condenser does not hold its chargecompletely over an entire pulse cycle. Thus, the derived D. C. voltageis a function of the rate at which the pulses occur. Resistor 3|, havinga high resistance value and which may be a conventional spark plugsuppressor, is provided to prevent excessive drain on the ignitionvoltage by the rectifier. The resistor 3| may be of the order of 10megohms.

As explained above, the gain control voltage is derived from theignition system of the automobile. In order to preserve simplicity ofdisclosure, a conventional type of ignition system has beenschematically shown. It is to be clearly understood that thisrepresentation of the ignition system is purely illustrative, and thatthe present invention encompasses the utilization of the various type ofignition systems employed in present day automobiles. Generallyspeaking, the ignition system comprises the direct current source l4having one terminal connected to one side of the primary winding ll ofthe induction coil through a path which includes the ignition key switchI9. The other terminal of the current source is connected to theopposite end of the primary winding through timer mechanism l8.Condenser 20, connected between one timer point I9 and ground, providesthe proper spark characteristics. The secondary winding 2| of theinduction coil has one end thereof at ground potential, whereas theopposite end is connected to the central point 22 of the sparkdistributor. The points 24 of the spark plugs are grounded. The numeral25 denotes one of the automobile engine cylinders. The distributorcomprises the contact points 4|, equally spaced in a circle and eachcorresponding to one of the spark plugs, and the rotatable arm 43. Thelatter is geared in any desired manner, and as conventionally shown at40, to the rotatable cam mechanism actuating timer |8 so that the latteropens as the arm 43 is positioned in line with a point 4|. Each contact4| is connected by a lead 5!] to the central point 23 of each sparkplug. The rotatable cam mechanism speed is, of course, a function of theengine speed.

The points 23 and 24 of the spark plug project into the interior of thecylinder 25, and the spark plug consists of two well insulated metallicpoints. The central point is usually connected to a binding post whichreceives the current from the secondary, or high tension, winding 2| ofthe induction coil IT. The point 24 is usually about $2- of an inchdistant from the point 23, and is separated from it by an air gap. Thesecond point 24 is grounded through the thread of the plug to the engineframe. When the switch I9'is closed a current from the source l4,usually a storage battery, flows through the timer mechanism, whichcompletes the circuit at the proper time through the induction. coil. Atthe time of breaking of contacts I9 a high voltage is induced in thesecondary 2|, which in turn produces a spark at the gap of the sparkplug thereby igniting the explosive mixture in the cylinder. The windingmaterial surrounding the core of the induction coil usually consists ofseveral turns of fairly large insulated copper wire, and this is theprimary winding IT. The secondary, or outside, winding 2| consists of alarge number of turns of very fine insulated wire. The abovedescription, in general, covers the ignition system of an automobile.

The cathode 9 of diode 8 is connected to the central point 23 of thespark plug through a path which includes condenser 30 and resistor 3|.The condenser 30 is sufficiently small in relation to the other circuitconstants so that the direct current control voltage developed acrossload resistor II is a function of the speed of the engine. By adjustingtap on load resistor H to a point on the latter which assumes a positivepotential with respect to ground, it will be seen that the signal grid 5has its normal negative bias reduced as the direct current voltagedeveloped across resistor increases in magnitude. This results in. anincrease in gain of the audio amplifier 4. The functioning of thepresent gain control system will now be clear from the above descriptionand the drawing.

Assuming that the automobile is not moving, or is moving'very slowly,there will be a minimum of control voltage developed across resistor Hby virtue of the fact that the voltage pulses produced between sparkplug points 23 and 24 per unit of time is a minimum. Hence, the audioamplifier 4 will have a normal gain determined by the bias value. Thisgain will be sufficient so that the volume level will be tolerable forlistening in the absence of extraneous noises which arise when a car ismoving with increasing speed.

However, as soon as the speed in increased, and the speed increasessufficiently to cause the well known wind noises, mechanical rattlingand engine noise, then the gain control system automatically functionsto increase the volume level of the receiver. This increase in voltagepulses is converted into an increased direct current voltage magnitudeacross load resistor due to the rectification action of diode 8-. Aspointed out before, as the control voltage across resistor increases thenormal negative bias on the signal grid of the tube decreases, and thegain of the amplifier is increased. The capacity 60 may be inserted inthe lead to the rectifier to filter out the radio frequency componentsof the ignition voltage pulses.

It is to be understood that the alternating current voltage supplied tothe rectifier 8 may also be derived from the secondary win-ding of theinduction coil prior to distribution, or from the primary side of theinduction coil, or even at the breaker. The exact circuit constantsemployed will be a function of the amount of control voltage required,the type of automobile, and the point on the ignition system from whichthe voltage pulses are obtained. It is, also, to be understood that thereceiver itself may be of the tunable radio frequency amplifier type,and need not be restricted to the superheterodyne type. Again, the gaincontrol need not be applied to an audio amplifier, but may be applied toany other signal transmission tube of the system; the only requisite isthat a gain control voltage be applied to the network of the receivingsystem which is capable of being regulated so as to materially changethe volume of the receiver. The control voltage may be applied, ifdesired, to an electrode other than the signal grid.

While I have indicated and described a system for carrying my inventioninto effect, it will be apparent to one skilled in the art that myinvention is by no means limited to the particular organization shownand described, but that many modifications may be made without departingfrom the scope of my invention, as set forth in the appended claims.

What is claimed is:

1. In combination with the ignition system of an automobile, a radioreceiver, means responsive to voltage pulses derived from the ignitionsystem for developing a uni-directional voltage which varies directlywith automobile speed, and means for automatically regulating the volumelevel of the receiver with said voltage in the same sense.

2. In an automobile of the type provided with a radio receiver, meansresponsive to increase in the rate of voltage pulses of the automobileignition system for developing a uni-directional voltage which variesdirectly with automobile speed,

and means for increasing the volume level of the receiver with saidvoltage as the speed of theautomobile engine increases.

3. In combination with the ignition system of an automobile engine, aradio receiver installed in the automobile and including at least onesignal transmission tube whose gain is to be controlled,

means responsive to the number of pulses per secnd of the alternatingvoltage at the ignition system for increasing the gain of saidtransmission tube.

4. In combination with the ignition system of an automobile engine, aradio receiver installed plugs of an automobile engine, a radio receiverinstalled in the automobile, means for'rectifying voltage pulses derivedfrom the spark plug, and

means for increasingthe volume level of the receiver in accordance withincrease of the unidirectional voltage output of said rectifier.

6. In an automobile provided with a radio receiver, a combustion engineemploying an electrical ignition system, the method which includesderiving an alternating current voltage from the automobile ignitionsystem, deriving a uni-directional gain control voltage from thealternating current voltage whose magnitude is directly dependent on theengine speed, and adjusting the volume level of the receiver in the samesense as the magnitude of the uni-directional voltage varies.

'7. In a mobile vehicle of the'type provided with a combustion engineemploying an electrical ignition system, the vehicle being provided witha radio receiver, the method which includes deriving a gain controlvoltage from the ignition system whose magnitude is a function of thespeed of the engine, and increasing the volume level of the receiverwith the derived voltage as the engine speed increases.

8. In an automobile having an ignition system and being provided with aradio receiver having at least one signal transmission tube to becontrolled in gain, a rectifier coupled to-the ignition system forproducing a uni-directional voltage whose magnitude increases with theautomobile engine speed increase, and means for applying theuni-directional voltage to said transmission tube in a sense to increasethe gain thereof and thereby increase the volume level of the receiverto an intensity such that the extraneous noises produced by the increasein speed of the auto-mobile are efiectively overcome.

JARRETT L. HATHAWAY.

